GPIO 1_24 output not driving correctly

Sean Machin

I have a custom AM335x based board and am trying to use GPIO1_24 as a simple digital output. On my board that signal is used to reset a modem module. I have a script that pulses the GPIO high for one second, then low for one second. However, when looking at the signal on the scope it pulses high for a very short amount of time, then does an exponential decay, see attached screenshot. I have the pin configured in the board file as:

static struct pinmux_config sundac_gpio_pin_mux[] = {
{"gpmc_ben1.gpio1_28", OMAP_MUX_MODE7 | AM33XX_PIN_OUTPUT}, // GPIO1_28 to enable u4 buffer
{"gpmc_a8.gpio1_24", OMAP_MUX_MODE7 | AM33XX_PIN_OUTPUT},// GPIO1_24 goes to modem reset via FET
{"gpmc_a9.gpio1_25", OMAP_MUX_MODE7 | AM33XX_PIN_OUTPUT},// GPIO1_25 goes to modem PWR_ON via FET
#;;;{NULL, 0},
};

GPIO 1_25 is also used as an output and it functions correctly. Any ideas?

over 12 years ago

0 Biser Gatchev-XID over 12 years ago

TI__Guru**** 393215 points

Hi Sean,

Can you post the pin connection part of the schematics? Also, have you checked that your pinmiux is not changed by other code somewhere?

0 Sean Machin over 12 years ago in reply to Biser Gatchev-XID

Intellectual 995 points

Full schematic as PDF is at http://resplendid.com/sundac_3-a.pdf

I double checked my board file pin mux settings and verified there is only one call to configuring GPIO1_24, as shown in the first post.

0 Biser Gatchev-XID over 12 years ago in reply to Sean Machin

TI__Guru**** 393215 points

Hi Sean,

Your FAE provided additional data on the internal forum about the modem board. Here is what I see:

From file "sundac_3-a.pdf": AM335X pin V16 (pin name GPMC_A8) -> signal GPIO1_24 -> GPIO_BUS4 -> GPRS0_6 -> J3000 pin 8 (pin name D8). Then from file "1222.CELLULAR MODEM_U-BLOX_SCHEMATIC_760-000016.pdf": J3 pin 8 (pin name D8) -> signal VGPRS_EN -> U5 pin 1 (pin name EN), with pullup 100kOhm to VBAT (R6). If VBAT is above VDDSHV3 (3.3V from VMMC) this can damage pin V16 of AM335X!!!

From file "1222.CELLULAR MODEM_U-BLOX_SCHEMATIC_760-000016.pdf": J3 pin 16 (pin name D16) -> SYS_RESETN -> Q1 gate. Then from file "sundac_3-a.pdf": J3000 pin 16 (pin name D16) -> RESET -> GPRS_RESET -> buffered by U46 -> SYS_RESETn -> SYS_WARMRESETn -> AM335X pin A10 (pin name WARMRSTn). This is the processor warm reset signal. It is a bi-directional signal. Please check section 8.1.7.4.1.1 of the AM335X TRM, Rev.I for description of this signal.

0 Sean Machin over 11 years ago in reply to Biser Gatchev-XID

Intellectual 995 points

Turns out that the exponential decay seen on the scope shot was a probe coupling problem.

Processors

Processors forum

GPIO 1_24 output not driving correctly